Semiconductor lasers and photodetectors used in optical fiber communication systems are usually hermetically sealed in a package to ensure long term reliability. The package must permit optical coupling of the packaged opto-electronic devices to cabled optical fibers which carry optical signals between the packaged opto-electronic devices.
One known package for opto-electronic devices comprises a housing having a cavity for receiving an opto-electronic device. A single optical fiber passes through a small hole in the housing and has one end aligned with and adjacent to the opto-electronic device. The other end of the fiber segment is attached to a cabled optical fiber by a connector or splice to optically couple the opto-electronic device to the cabled fiber. The hole must be sealed around the optical fiber segment to ensure that the housing is hermetically sealed.
Unfortunately, it is difficult and time-consuming to align the optical fiber segment to the opto-electronic device and to secure the optical fiber segment in that alignment. Specialized alignment equipment and skilled operators are required to achieve the desired alignment, and this contributes significant capital and labour costs to the total cost of the packaged devices. The end of the optical fiber segment may require special treatment to form a taper or ball lens for improved coupling efficiency, and this adds further to equipment and labour costs. Moreover, to maintain accurate alignment, the fiber is generally secured at a point inside the housing in addition to being secured by the seal at the hole in the housing. Differential expansion of the fiber segment and the housing due to temperature shifts can cause breakage of the fiber segment.
Another known package for opto-electronic devices comprises a housing having a transparent window in the form of a glass or sapphire plate. The opto-electronic device inside the housing is optically coupled to an optical fiber outside the housing through the window. Using conventional assembly procedures and tolerances, the opto-electronic device is generally at least 400 microns from the end of the optical fiber outside of the housing.
The relatively large gap between the opto-electronic device and the fiber end causes an unacceptable coupling loss for many applications unless a focussing lens is disposed between the opto-electronic device and the optical fiber end. The focussing lens adds to the cost of the package. Moreover, the lens must be aligned with the opto-electronic device and the optical fiber, and must be secured in that alignment. This requires sophisticated lens mounting arrangements, specialized alignment equipment and skilled operators, adding further to the total package cost.
Some known packages for opto-electronic devices are designed to mate with standard optical fiber connectors to optically couple the opto-electronic device to an optical fiber. In the dominant connector types (e.g. the ST, SC and FC connector types), optical fibers to be connected are centered in spring-loaded ferrules. Many connectorized packages for opto-electronic devices have a recess for receiving and aligning a connector ferrule such that the optical fiber carried by the ferrule is optically coupled to the opto-electronic device, usually via a lens.
The end of the ferrule must be properly positioned with respect to the lens (usually at the focal point of the lens) for optimum coupling. To ensure proper positioning of the ferrule, the ferrule is urged by its spring against a stop formation of the receptacle, the stop formation being precisely positioned relative to the lens. Often the stop formation engages a chamfered edge of the ferrule. Unfortunately, while the diameter of these ferrules is standardized at 2.5 mm, the degree of chamfer is not standardized, and ferrules with different chamfers are urged into different positions in the receptacle, resulting in different coupling efficiencies.